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The Fatty Acid method was used to determine whether incorporation of plasma radiolabeled arachidonic acid into brain phospholipids is controlled by phospholipase A2. Awake rats received an i.v. injection of a phospholipase A2 inhibitor, manoalide (10 mg/kg), and then were infused i.v. with [1-14C]arachidonate or [3H]arachidonate. Animals were killed after infusion by microwave irradiation, and tracer distribution was analyzed in brain phospholipid, neutral lipid and acyl-CoA pools. Calcium-independent phospholipase A2 activity in brain homogenate was reduced by manoalide, whereas phospholipase C activity was unaffected. At 60 min but not at 20 or 40 min after its injection, manoalide had significantly decreased by 50% incorporation of unesterified arachidonate into and turnover within brain phospholipids, taking into account dilution of the brain arachidonoyl-CoA pool by recycled arachidonate. Manoalide also increased by 100% the net rate of unesterified arachidonate incorporation into brain triacylglycerol. This study indicates that manoalide can be used to inhibit brain phospholipase A2 in vivo, and that phospholipase A2 plays a critical role in arachidonate turnover in brain phospholipids and neutral lipids.